You might be glad of some maternity jumpers as while you will be mainly pg in the summer, it is the last month or two that nothing seems to fit. If you like cardis normally then that will do nicely though, in my case I did get some longer ones as the band on mat jeans is minging and all my tops seem to ride up at the back. Tighter styles are definitely more flattering than tents and just as comfy.
I live in jeans so when I finally found some that stayed put, I got 2. Also have a few pairs of linen trousers as it is finally getting warm, due in 6 weeks. Vest tops with casual pre-pg shirts or cardis over the top.
My 'investments' were pyjamas! I have 3 pairs as they seem to need washing a lot, getting hot at night I guess. And it has ended up as a mix of long and short sleeve tops. Hospitals are saunas so short sleeve or vests are better I think. Also I have made sure that underwear fits properly, so new bras at around 20 weeks when suddenly I gained 3 cup sizes overnight, but they've been fine since. Pretty and underwired are fine if they fit correctly, and made me feel so much happier once my bump and boobs were separated again lol! Also got some bra back extenders from a sewing shop as my ribs are now spreading but no need to change cup size. Wait to get feeding bras until your milk has come in if you can, or some places do offer an advance service, but in my last pg I seemed to change daily until the feeding was really established, ended up with all sorts of sizes going on. It can get expensive if you find you change a lot.
If you know what size you need then ebay can be a complete bargain, there's not much resale value in mat clothes, but they are often hardly worn. My experience has been that a size smaller is often fine, so many are cut like tents. For example I would normally wear a 10 trouser in Next but my mat trousers are an 8, the 10s were massive. Or look for adjustable waists and you are more likely to get a bargain.